The present invention relates to the production of soft laser light and line laser light, and their uses in various fields. One major field of use is spectrophotometers and scanning densitometers. Other uses are communication, detection, photography, microscopy, movies and television and others. The major one particular use is scanning densitometry where high resolution and sensitivity are improved by using the soft and/or line laser.
Methods of protein separation have improved greatly while quantitation by densitometry has lagged behind. Disc electrophoresis on polyacrylamide gel achieves a high resolution that could be qualitatively observed but no available scanning densitometer can do the pattern recording. Bands appearing separated by visual observation reveals overlapping peaks. The resolution obtained on gel is partially or significantly lost upon scanning. The complex pattern obtained by isoelectric focusing calls for further improvement of scanners resolution. ICEP has further increased the requirement of higher resolution.
Disc electrophoresis needs scanning densitometers of 100.mu. resolution. Isoelectric focusing on polyacrylamide gel needs 50.mu. resolution and so does ICEP. In order to make isoelectric focusing scannable by present instruments LKB Company, the inventors, changed to sheet rather than tube isoelectric focusing. Upon drying, the bands of separated proteins by isoelectric focusing plate, shrink to a thin film and scanning has less chance to lose resolution. But still the pattern is very complex and regular light scanning densitometry still loses the resolution which could be seen by the naked eye.
An attractive present trend to improve resolution is to use the microscope system in order to detect transmitted light through narrow areas but light diffraction made this system of very limited use. The resolution is improved slightly, but the background noise is increased.
The most successful system so far is to take a picture and scan the transparent negative film with double microscope system. One lens system focuses the light and converges it to a spot at the plane of the negative. The second miscroscope detects and quantitates the transmitted light through the spot, not the diffracted portion, and focuses it on a photodetector. This is a very tedious and time consuming process. The resolution is still lost (a) during picture taking, where focusing is on a limited area only and (b) diffraction and scattering of regular light still imposes the limited resolution.
Another approach is the photon counting system in which a narrow slit lowers the light intensity, and this is accompanied by less diffraction. The background noise increases and the stained protein bands are relatively too dark. Thus, Beer's law does not hold for optical density quantitation.